BERYLLIUM COPPER ALLOY HAVING HIGH STRENGTH, MACHINABILITY AND HEAT RESISTANCE AND PRODUCTION METHOD THEREOF

Abstract: An alloy containing a relatively small amount of Be to decrease its deformation when heat-treated. The decrease in strength of the alloy due to the decreased Be content is compensated for by Si and Al solid solution hardening and NiBe and CoBe precipitation hardening. The precipitation of such intermetallic compounds also improves machinability and heat resistance and allows the aging conditions to be more flexible. Therefore, the present invention can economically provide a beryllium copper alloy having excellent strength, machinability and heat resistance and particularly, can drastically reduce a burden on the user side as to an aging material.

Description: Technical Field The present invention relates to beryllium-copper alloys used as electrically conductive spring materials for lead frames, terminals, connectors, relays, switches, jacks and the like, of which such properties as strength, workability and stress-relaxation are important, and a method for producing the same. Background Art Beryllium-copper alloys containing 0.2 to 0.3 % by weight of Be in copper are known as electrically conductive spring materials and disclosed in JP-B-4-53936 by the present applicant. As examples of such beryllium-copper alloys, there are aging materials of which an aging treatment is performed by users, and mill-hardened materials to which aging treatment has been applied before shipping. In US 4792365, a process is disclosed for the production of beryllium-copper alloys comprising 0.05 to 2.0 % by weight of Be, 0.1 to 10 % by weight of at least one of Co and Ni, optionally 0.05 to 4 % of at least one of Si, Al, Mg, Zr, Sn and Cr in total amount and the balance substantially Cu. The process involves casting, solution heat treatment at 800-1000°C, cold working, annealing at 750-950°C and age hardening. Recently, due to an enhanced miniaturization of electronic parts, higher strength is required also for beryllium-copper alloys. The material to be obtained is disclosed in JIS C 1720 (Be 1.8 to 2.0 % by weight). However, in these aging materials of such beryllium-copper alloys, there have been disadvantages that deformation is likely to occur during aging treatment and also setting up of treating conditions is difficult due to narrow tolerance of aging treatment conditions. Therefore, there has been a problem that it is not necessarily easy to attain the desired characteristics by aging treatment at the user's side. Also, in conventional mill-hardened beryllium-copper alloys, there have been problems that a sufficient workability cannot be obtained and, in particular, bending workability is poor in a direction perpendicular to the direction of rolling. Further, as to heat resistance that can be regarded as an index of long-term reliability, there has been a problem that stress-relaxation ratio is large. The stress-relaxation ratio is a value indicating reduction of spring properties over a long period of time and the measuring method thereof is regulated in EMAS (Japan Electronic Manufacturers Association Standard)-3003 "Testing Method of Stress-Relaxation by Bending of Spring Materials". According to this standard, the stress-relaxation is defined as a phenomenon that the stress generated in materials under a constant strain decreases slowly with a lapse of time. Disclosure of the Invention The present invention seeks to solve the above-mentioned problems advantageously. It is an object of the invention to provide a beryllium-copper alloy which is excellent in strength as a matter of course, which can be used as an aging material having a wide tolerance of the aging treatment conditions, i.e., flexible treatment conditions so as to reduce the burden at the user end by making deformation at the aging treatment difficult, and which can be also used as a mill-hardened material having excellent workability and heat resistance. It is a further object of the invention to provide an advantageous method for producing the same. According to the present invention, there is provided a beryllium-copper alloy as set out in claim 1. Also, the present invention provides a method for producing a beryllium-copper alloy as set out in claim 2. In the present invention, strength, workability and heat resistance to be attained as target are as follows. First, as to strength, tensile strength of should be 840 to 1150 MPa (84 to 115 kgf/mm 2 ). As for workability, at the tensile strength of 840 to 970 MPa (84 to 97 kgf/mm 2 ), when bending work is performed with a R/t ratio (R: bending radius, t: plate thickness) of 1.0, it should be possible to perform good work in any direction with respect to the direction of rolling. Further, as to heat resistance, that is, a heat treatment deformation amount, a deformed amount (change in warpage amount) of a material before and after aging treatment of a material having a size of 20 mm x 20 mm, and a plate thickness of 0.3 mm should be 10 µm or less. Furthermore, flexibility of the heat treatment conditions in accordance with the present invention should be such that fluctuation of tensile strength is within the range of ± 80 MPa (8 kgf/mm 2 ) even when optional aging conditions are selected. In the following, the present invention will be explained specifically. The first characteristic feature of the beryllium-copper alloy of the present invention resides in that, in order to reduce deformation due to heat treatment, the content of Be is made 1.5 % by weight or less which is markedly reduced as compared with the conventional beryllium-copper alloy. Nevertheless, when the content of Be is less than 0.5 % by weight, strength is insufficient since a strengthening mechanism is not effective. Accordingly, in the present invention, the content of Be is limited in the range of 0.5 to 1.5 % by weight. The more preferred range of Be is 0.7 to 1.3 % by weight, and a further preferred range is 0.9 to 1.1 % by weight. The second characteristic feature of the beryllium-copper alloy of the present invention resides in that lowering in strength accompanied by decreasing the content of Be as mentioned above is compensated by composite addition of Si, Al and Ni, Co. First, explanation will be made of Si and Al. These are each dissolved in the Cu mother phase as a solid solution and contribute to improvement in strength by solid solution strengthening mechanism. However, when their content is less than 0.5 % by weight, strength and workability are insufficient, while when the content exceeds 2.5 % by weight, conductivity, rolling workability and soldering property are lowered and also deformation due to heat treatment is promoted. Accordingly, Al and Si are to be contained in the range of 0.5 to 2.5 % by weight in either single use or in combination. The more preferred range is 1.0 to 2.5 % by weight, and a further preferred range is 1.5 to 2.5 % by weight. Next, explanation will be made of Ni and Co. These precipitate in the Cu mother phases as an intermetallic compound such as NiBe or CoBe, etc., and contribute to improvement in strength due to their precipitation strengthening mechanisms. And yet, by precipitation of such an intermetallic compound, heat resistance, etc. are also improved. When precipitation strengthening is intended by an intermetallic compound mainly comprising the above-mentioned NiBe or CoBe, if the content of Ni or/and Co is less than 0.3 % by weight, not only is strength lowered but also grain size becomes coarse whereby workability becomes poor. On the other hand, when the content of Ni or/and Co exceeds 1.5 % by weight, the amount of the intermetallic compound formed between Be, Si, Al, etc. increases whereby bending workability becomes poor. Accordingly, Ni and Co should be contained in the range of 0.3 to 1.5 % by weight in either single use or in combination. The more preferred range is 0.3 to 1.1 % by weight, and a further preferred range is 0.3 to 0.7 % by weight. Also, it is necessary that the amount of NiBe, CoBe intermetallic compounds to be precipitated, is in the range of 0.20 to 0.90 % by weight. The reason is that when the content is less than 0.20 % by weight, sufficient strength cannot be obtained, while when it exceeds 0.90 % by weight, bending workability is markedly lowered and heat resistance is also lowered. Accordingly, the more preferred amount of the intermetallic compound mainly comprising NiBe and CoBe is in the range of 0.20 to 0.60 % by weight when it is used as a mill-hardened material, whereas it is in the range of 0.30 to 0.75 % by weight when it is provided as an aging material. Further, in the NiBe and CoBe intermetallic compounds, size of the precipitate, i.e, grain size is important. The reason is that even when the content of the intermetallic compounds satisfy the above-mentioned preferred range, if the ratio of grains exceeding 0.1 µm is large, cracks are likely to be caused at working due to such coarse grains. Thus, in the present invention, at least 45% of these intermetallic compounds should be present as fine particles with a diameter of 0.1 µm or less. As stated above, in the present invention, in order to make compatible all of strength, bending workability and heat resistance, etc., characteristics such as strength and bending workability, etc. are improved by Be, Si and Al. Also, in the present invention, in order to suppress deformation in shape of the material at aging treatment, the amount of Be is decreased. As for lowering in strength accompanied by decrease in Be, properties are improved by precipitation strengthening of the intermetallic compounds mainly comprising NiBe and CoBe, and solid solution strengthening owing to Si, Al and the like. Incidentally, among the intermetallic compounds mainly comprising NiBe and CoBe, an intermetallic compound such as NiAl 3 , NiSi, etc. are also included in a little amount. Also, in addition to the above-mentioned components, Fe, Ti and Cr, may be added as a subcomponent in the range of 0.05 to 0.5 % by weight. These are components each of which contributes to improve strength, and particularly, Fe and Si are components which also contribute to improve workability. The third characteristic feature of the beryllium-copper alloy of the present invention resides in that heat treatment conditions are made flexible. The reason is that the precipitation temperature of NiBe or CoBe has an extremely wide temperature range of 300 to 460°C, and the treatment time also has extremely wide range of 15 minutes to 6 hours. And yet, even when in such wider treatment conditions, the variation range of tensile strength can be made within the range of ± 80 MPa (8 kgf/mm 2 ). As a result, the aging treatment at the user side becomes markedly easy as compared with prior art and the user's burden can be remarkably reduced. Next, preferred preparation conditions of the present invention will be explained. The cast piece prepared with the above-mentioned preferred composition range of components is subjected to hot working and/or cold working. The alloy of the present invention has essentially good hot workability and cold workability as long as it satisfies the above-mentioned composition range of the components. Then, a solution treatment is carried out in order that elements forming intermetallic compounds such as NiBe, CoBe, etc. are sufficiently dissolved in the mother phase as a solid solution. In this solution treatment, if the treatment temperature is less than 880°C, dissolution of elements forming intermetallic compounds into the alloy becomes insufficient and bending workability of the product becomes poor, so that it is necessary to set the solution treatment temperature as 880°C or higher. After the above solution treatment, the alloy is cooled to normal temperature. In the present invention, with regard to such a cooling treatment, it is important to carry out the cooling at a rate of 20°C/s or more, for at least the temperature range of 800°C to 600°C. The reason is that the temperature range of 800 to 600°C is a range in which intermetallic compounds such as NiBe, CoBe, etc., are likely precipitated with a coarse grain. Thus, if the cooling rate is slower than 20°C/s, most part of the intermetallic compounds precipitates as coarse grains, and as a result, precipitation of fine grains with a sufficient amount in the subsequent aging treatment cannot be expected. Such coarse grains make workability poor. Accordingly, in the present invention, after the solution treatment, the cooling should be carried out at a rate of 20°C/s or more for at least the temperature range of 800 to 600°C. More preferably, it is 40°C/s or more. Incidentally, the above-mentioned quenching treatment after the solution treatment is not limited only to the temperature range of 800 to 600°C, but it is needless to say that the same quenching treatment thereafter, for example, until room temperature, is advantageous for maintaining a sufficient amount of solid solution of the elements for forming an intermetallic compound. Here, as for cooling means, any means are effective as long as the above-mentioned cooling rate can be ensured, and it is not particularly limited. Thus, water cooling, mist cooling, gas cooling, etc. are particularly advantageously adopted. Then, finishing work is carried out to finish the alloy to a shape of a product. At this time, if the working ratio is less than 5 %, sufficient strength cannot be obtained, while if it exceeds 40 %, bending workability deteriorates so that the working ratio is limited to the range of 5 to 40 %. The more preferred working ratio is 10 to 20 %. Subsequently, an aging treatment is carried out to precipitate a desired intermetallic compound. Here, when the aging temperature is less than 300°C, sufficient strength cannot be obtained or, even when obtained, bending workability deteriorates. On the other hand, if it exceeds 460°C, bending workability also deteriorates. Thus, it is necessary to set the aging temperature in a range of 300 to 460°C. Also, the aging time can be selected from a wide range of 15 min to 6 hours. More preferred aging treatment conditions are the temperature of 320 to 380°C and the time of 20 min to 3 hours, and further preferred treatment conditions are the temperature of 330 to 360°C and the time of 1 to 3 hours. Thus, it is possible to obtain a beryllium-copper alloy which has little heat treatment deformation in an aging treatment, is flexible in the aging treatment conditions, and yet has excellent strength, bending workability and heat resistance. Brief Description of the Drawing Fig. 1 is a graph showing the relationship between aging treatment time and tensile strength of the obtained product, with an aging treatment temperature as a parameter. Best Mode for Carrying Out the Invention Example 1 This example relates to mill-hardened materials, in which cast pieces of beryllium-copper alloys having the compositions each shown in Tables 1 to 7 were subjected to solution treatment, finishing working and then aging treatment under the conditions shown in these Tables to prepare products. The results were examined for stress relaxation ratio, hardness, tensile strength and bending workability of the thus obtained products, and are also shown in Tables 1 to 7 with overall evaluations. Incidentally, the bending workability was judged by eye by subjecting a test specimen having a plate thickness of 0.3 mm to bending working using a bending tool so that the inner bending radius come to 0.3 mm, (R/t ratio = 1.0) in accordance with JIS Z 2248, then the bent surface was observed by magnifying it by 30 times. The directions of bending were made parallel direction (0°) and perpendicular direction (90°) to the direction of rolling, and expressed by o ○: no rough, O: a little rough, Δ: markedly rough, ×: cracks, and ××: rupture. Also, to determine the amount of material deformation, small specimens with a size of 20 x 20 mm were cut from the material having a plate thickness of 0.3 mm in both longitudinal and width directions, and the amounts of curvature were measured before and after heat treatment. For measurement of the amounts of curvature, a non-contact type shape measuring device was used. Further, for the heat resistance, among the properties of the materials thus obtained, the stress relaxation ratio (permanent deformation amount) was obtained by measurement using the cantilever beam method by loading with stress of 80 % or less of 0.2 % proof stress at 200°C for 100 hours. Mill-hardened materials Examples Number 1 2 3 4 5 6 7 Composition wt % Be 0.9 0.7 1 0.9 1.11 1.11 1.29 Ni 0.6 0.8 0.87 0.8 0.27 0.4 0.6 Co 0 0.07 0 0.07 0.6 0.47 0.27 Al 0.5 1.5 1 1 0.9 0.2 0.5 Si 0.5 0.8 0 0 0.5 1 0.5 NiBe+CoBe (theoretical value) 0.69 1.00 1.00 1.00 1.00 1.00 1.00 NiBe+CoBe (precipitated amount) 0.39 0.82 0.54 0.52 0.57 0.60 0.67 Ratio of fine particle (%) 92 48 62 71 60 58 51 Preparation conditions Solution treatment temperature (°C) 910 905 900 910 900 900 885 Cooling temperature (°C/s) 45 25 30 35 30 30 25 Aging temperature (°C) 340 360 345 350 345 345 340 Aging time (min) 20 80 15 10 15 20 15 Working ratio (%) 15 20 20 20 20 20 25 Properties Stress relaxation ratio (%) 10 12 13 14 15 14 18 Hardness (Hv) 241 288 247 245 285 272 276 Tensile strength (kgf/mm 2 ) 84.5 94.6 86.7 86 94.2 95.4 96.8 Bending workability (0°) o ○ ▵ o ○ o ○ ○ ○ ▵ Bending workability (90°) o ○ ▵ o ○ o ○ ○ ○ ▵ Overall evaluation very good good very good very good very good very good good Mill-hardened materials Examples Number 8 9 10 11 12 13 14 Composition wt % Be 1.29 0.9 0.9 1.11 1.11 0.7 0.7 Ni 0 1.05 0 0.5 0.5 0.2 0.4 Co 0.87 0 1.05 0.55 0.55 0.3 0.1 Al 1.5 0.5 0.8 0 1 2 0.5 Si 0.9 1.2 0 0.6 1.1 0.2 0.9 NiBe+CoBe (theoretical value) 1.00 1.00 1.21 1.21 1.21 0.58 0.58 NiBe+CoBe (precipitated amount) 0.65 0.79 0.72 0.72 0.77 0.41 0.40 Ratio of fine particle (%) 53 55 61 72 49 60 70 Preparation conditions Solution treatment temperature (°C) 890 900 915 905 895 905 910 Cooling temperature (°C/s) 25 25 30 35 25 30 35 Aging temperature (°C) 340 360 360 350 350 340 340 Aging time (min) 15 15 10 20 30 35 20 Working ratio (%) 35 30 18 36 25 20 20 Properties Stress relaxation ratio (%) 18 14 15 17 13 14 16 Hardness (Hv) 290 284 251 255 287 288 251 Tensile strength (kgf/mm 2 ) 95.9 96.6 88 89.5 93.6 94.2 88.1 Bending workability (0°) ○ ▵ ○ ○ ▵ ○ o ○ Bending workability (90°) ▵ ▵ ▵ ○ ▵ ▵ o ○ Overall evaluation good good good good good good good Mill-hardened materials Examples Number 15 16 17 18 19 20 21 22 Composition wt % Be 0.98 0.98 1.3 0.81 1.08 1.3 0.92 1.05 Ni 0.52 0.4 0.49 0.32 0.31 0.1 0.46 0.45 Co 0 0.12 0 0 0 0.39 0 0 Al 0 2.1 0 2.0 2.0 2.0 1.9 1.9 Si 0.8 0.3 0.8 0 0 0.3 0 0 NiBe+CoBe (theoretical value) 0.60 0.60 0.57 0.37 0.36 0.57 0.53 0.52 NiBe+CoBe (precipitated amount) 0.35 0.40 0.35 0.20 0.22 0.37 0.35 0.32 Ratio of fine particle (%) 91 72 59 62 86 60 81 75 Preparation conditions Solution treatment temperature (°C) 905 895 890 910 905 880 910 905 Cooling temperature (°C/s) 45 35 25 30 45 25 45 40 Aging temperature (°C) 340 340 340 340 340 340 340 340 Aging time (min) 15 60 45 20 20 30 20 30 Working ratio (%) 25 25 20 20 20 20 12 20 Properties Stress relaxation ratio (%) 9 8 11 10 4 10 8 8 Hardness (Hv) 240 290 257 240 259 290 289 291 Tensile strength (kgf/mm 2 ) 84.2 96.9 90.2 84.2 90.4 96.3 89.9 90.0 Bending workability (0°) o ○ ○ ○ o ○ o ○ ○ o ○ o ○ Bending workability (90°) o ○ ▵ ○ ○ o ○ ▵ o ○ ○ Overall evaluation very good very good good good very good good very good very good Mill-hardened materials Comparative Examples (Component) Number 1 2 3 4 5 6 Composition wt % Be 0.47 0.47 0.47 0.47 1.06 1.06 Ni 2 0.97 0 0.2 0.7 1 Co 0.47 0.5 0.97 0.77 0.69 0.39 Al 0.2 1.5 0 3 3.5 0 Si 0 0.5 0.5 0.6 1.5 0.1 NiBe+CoBe (theoretical value) 1.70 1.70 1.12 1.12 1.60 1.60 NiBe+CoBe (precipitated amount) 0.78 0.50 0.25 0.75 1.15 0.75 Ratio of fine particle (%) 2 25 7 18 11 4 Preparation conditions Solution treatment temperature (°C) 915 905 915 905 890 905 Cooling temperature (°C/s) 1 15 5 10 5 2 Aging temperature (°C) 380 380 380 380 360 360 Aging time (min) 30 40 30 30 60 20 Working ratio (%) 20 20 20 20 20 20 Properties Stress relaxation ratio (%) 21 19 22 26 21 24 Hardness (Hv) 148 251 161 266 289 198 Tensile strength (kgf/mm 2 ) 51.9 88.1 56.5 89.3 89.2 69.5 Bending workability (0°) ○ × o ○ × ×× ▵ Bending workability (90°) ▵ ×× ○ ×× ×× × Overall evaluation Poor strength Poor workability Poor strength Poor workability Poor workability Poor strength Mill-hardened materials Comparative Examples (Component) Number 7 8 9 10 11 Composition wt % Be 1.54 1.56 1.69 1.69 1.05 Ni 0.2 0.11 1.1 0 0.15 Co 0.41 0.5 0.11 1.2 0 Al 0.1 1.5 0.2 0 0 Si 0.3 1 0 0.8 0.9 NiBe+CoBe (theoretical value) 0.70 0.70 1.40 1.40 0.17 NiBe+CoBe (precipitated amount) 0.43 0.46 1.05 1.02 0.09 Ratio of fine particle (%) 40 21 38 12 65 Preparation conditions Solution treatment temperature (°C) 870 860 865 860 905 Cooling temperature (°C/s) 20 10 20 5 30 Aging temperature (°C) 340 340 345 345 350 Aging time (min) 40 60 40 15 15 Working ratio (%) 20 15 20 25 20 Properties Stress relaxation ratio (%) 20 15 16 14 22 Hardness (Hv) 254 290 265 288 201 Tensile strength (kgf/mm 2 ) 89.1 96.8 93 94.3 70.1 Bending workability (0°) ▵ ×× ▵ × o ○ Bending workability (90°) ×× ×× × ×× o ○ Overall evaluation High cost Poor workability High cost Poor workability Poor strength Example 2 This example relates to aging materials, in which cast pieces of beryllium-copper alloys having the compositions each shown in Tables 8 to 12 were subjected to solution treatment, finishing working and then aging treatment under the conditions shown in said Tables to prepare products. The results were examined for stress relaxation ratio, hardness, tensile strength and bending workability of the thus obtained products, and are also shown in Tables 8 to 12 with overall evaluations. Aging materials Examples Number 1 2 3 4 5 6 7 Composition wt % Be 0.9 0.7 1 0.9 1.11 1.11 1.29 Ni 0.6 0.8 0.87 0.8 0.27 0.4 0.6 Co 0 0.07 0 0.07 0.6 0.47 0.27 Al 0.5 1.5 1 1 0.9 0.2 0.5 Si 0.5 0.8 0 0 0.5 1 0.5 NiBe+CoBe (theoretical value) 0.69 1.00 1.00 1.00 1.00 1.00 1.00 NiBe+CoBe (precipitated amount) 0.60 0.74 0.73 0.69 0.71 0.71 0.76 Ratio of fine particle (%) 92 48 62 71 59 61 50 Preparation conditions Solution treatment temperature (°C) 910 905 900 910 900 900 885 Cooling temperature (°C/s) 45 25 30 35 30 30 25 Aging temperature (°C) 340 360 345 350 345 345 340 Aging time (min) 300 100 180 120 90 90 120 Working ratio (%) 15 20 20 20 20 20 25 Properties Stress relaxation ratio (%) 7 9 10 12 12 13 16 Hardness (Hv) 283 330 297 286 325 322 356 Tensile strength (kgf/mm 2 ) 99.3 110 104 99.6 109 109 111 Deformation amount (µm) 3 4 5 4 4 4 6 Overall evaluation very good good good very good very good very good good Aging materials Examples Number 8 9 10 11 12 13 14 Composition wt % Be 1.29 0.9 0.9 1.11 1.11 0.7 0.7 Ni 0 1.05 0 0.5 0.5 0.2 0.4 Co 0.87 0 1.05 0.55 0.55 0.3 0.1 Al 1.5 0.5 0.8 0 1 2 0.5 Si 0.9 1.2 0 0.6 1.1 0.2 0.9 NiBe+CoBe (theoretical value) 1.00 1.21 1.21 1.21 1.21 0.58 0.58 NiBe+CoBe (precipitated amount) 0.65 0.88 0.69 0.72 0.89 0.51 0.46 Ratio of fine particle (%) 51 48 61 70 52 63 71 Preparation conditions Solution treatment temperature (°C) 890 900 915 905 895 905 910 Cooling temperature (°C/s) 25 25 30 35 25 30 35 Aging temperature (°C) 340 360 360 350 350 340 340 Aging time (min) 50 120 60 50 180 240 200 Working ratio (%) 35 30 18 36 25 20 20 Properties Stress relaxation ratio (%) 15 12 12 15 11 12 13 Hardness (Hv) Tensile strength 340 339 276 283 335 342 300 (kgf/mm 2 ) 109 107 96.8 99.9 111 110 105 Deformation amount (µm) 7 5 4 4 5 6 2 Overall evaluation good good good good good good good Aging materials Examples Number 15 16 17 18 19 20 21 Composition wt % Be 0.98 0.98 1.3 0.81 1.08 0.92 1.05 Ni 0.52 0.4 0.49 0.32 0.31 0.46 0.45 Co 0 0.12 0 0 0 0 0 Al 0 2.1 0 2.0 2.0 1.9 1.9 Si 0.8 0.3 0.8 0 0 0 0 NiBe+CoBe (theoretical value) 0.60 0.60 0.57 0.37 0.36 0.53 0.52 NiBe+CoBe (precipitated amount) 0.41 0.41 0.39 0.31 0.30 0.41 0.40 Ratio of fine particle (%) 91 72 51 62 90 89 83 Preparation conditions Solution treatment temperature (°C) 905 895 890 910 905 910 905 Cooling temperature (°C/s) 45 35 25 30 45 45 40 Aging temperature (°C) 340 340 340 340 340 340 340 Aging time (min) 160 50 100 120 120 120 120 Working ratio (%) 25 25 20 20 20 12 20 Properties Stress relaxation ratio (%) 7 5 8 8 4 4 4 Hardness (Hv) 275 347 308 300 275 270 275 Tensile strength (kgf/mm 2 ) 96.5 112 106 104 96.0 95.9 96.4 Deformation amount (µm) 3 3 5 2 3 3 3 Overall evaluation very good very good good good very good very good very good Aging materials Comparative Examples Number 1 2 3 4 5 6 Composition wt % Be 0.47 0.47 0.47 0.47 1.06 1.06 Ni 1 0.97 0 0.2 0.7 1 Co 0.47 0.5 0.97 0.77 0.69 0.39 Al 0.2 1.5 0 3 3.5 0 Si 0 0.5 0.5 0.6 1.5 0.1 NiBe+CoBe (theoretical value) 1.70 1.70 1.12 1.12 1.60 1.60 NiBe+CoBe (precipitated amount) 0.71 1.10 0.56 0.76 0.98 1.05 Ratio of fine particle (%) 2 29 9 38 10 21 Preparation conditions Solution treatment temperature (°C) 915 905 915 905 890 905 Cooling temperature (°C/s) 1 15 5 20 5 10 Aging temperature (°C) 380 380 380 380 360 360 Aging time (min) 60 120 100 100 60 300 Working ratio (%) 20 20 20 20 20 20 Properties erties Stress relaxation ratio (%) 18 17 21 22 19 21 Hardness (Hv) 198 269 211 300 276 248 Tensile strength (kgf/mm 2 ) 69.2 94.4 74 99.8 97.1 87 Deformation amount (µm) 2 4 2 15 17 3 Overall evaluation Poor strength Poor strength Poor strength Excees deformation Excess deformation Poor strength Aging materials Comparative Examples Number 7 8 9 10 Composition wt % Be 1.54 1.56 1.69 1.69 Ni 0.2 0.11 1.1 0 Co 0.41 0.5 0.11 1.2 Al 0.1 1.5 0.2 0 Si 0.3 1 0 0.8 NiBe+CoBe (theoretical value) 0.70 0.70 1.40 1.38 NiBe+CoBe (precipitated amount) 0.47 0.50 0.97 0.91 Ratio of fine particle (%) 1 18 4 11 Preparation conditions Solution treatment temperature (°C) 870 860 865 860 Cooling temperature (°C/s) 1 10 2 5 Aging temperature (°C) 340 340 345 345 Aging time (min) 90 120 100 60 Working ratio (%) 20 15 20 25 Properties Stress relaxation ratio (%) 18 13 13 13 Hardness (Hv) 295 298 301 310 Tensile strength (kgf/mm 2 ) 99.5 100 102 104 Deformation amount (µm) 11 15 18 20 Overall evaluation Excess deformation Excess deformation Excess deformation Excess deformation Example 3 An alloy cast piece having the composition 0.8 % by weight of Be, 0.8 % by weight of Ni, 0.07 % by weight of Co and 1.0 % by weight of Al, and the balance being substantially Cu was subjected to hot working and then cold working according to a conventional method. After solution treatment at 910°C, the cast piece was immediately cooled to room temperature at a rate of 40°C/s. Then, after subjecting the cast piece to finishing working with a working ratio of 20 %, aging treatment was carried out with various conditions. The results of the tensile strength measured with respect to the thus obtained products are shown in Fig. 1. It can be clearly seen from the figure that, in the present invention, good tensile strength can be obtained with wide aging treatment conditions. Particularly, when it is carried out under preferred conditions at a temperature of 320 to 380°C, excellent tensile strength could be obtained. Industrial Applicability The beryllium-copper alloy of the present invention is advantageous in that it has high strength and excellent bending workability, and yet deformation amount at heat treatment is small even though the contents of expensive Be is lowered than conventional products. Also, the beryllium-copper alloy of the present invention has wide tolerable aging treatment conditions, and as shown in Fig. 1, when it is within the temperature range of 320 to 380°C, even if the aging treatment time is substantially changed in the range of 15 minutes to 6 hours, change in tensile strength can be regulated within the range of ± 80 MPa (8 kgf/mm 2 ). Therefore, the present invention provides advantages that not only an electrically conducting spring material having excellent properties can be realized economically, but also the users' burden for aging treatment carried out by themselves can be markedly reduced.

Claims: A beryllium-copper alloy, having the composition:- 0.5 to 1.5 % by weight of Be; 0.3 to 1.5 % by weight in total of at least one of Ni and Co; 0.5 to 2.5 % by weight in total of at least one of Si and Al; optionally 0.05 to 0.5 % by weight of strengthening elements selected from Fe, Ti and Cr; and the balance being Cu and inevitable impurities; said alloy containing as an intermetallic compound NiBe and/or CoBe in the range of 0.20 to 0.90 % by weight of which at least 45 % is present as fine particles having a diameter of 0.1 µm or less. A method for producing a beryllium-copper alloy which comprises casting a material having the composition:- 0.5 to 1.5 % by weight of Be; 0.3 to 1.5 % by weight in total of at least one of Ni and Co; 0.5 to 2.5 % by weight in total of at least one of Si and Al; optionally 0.05 to 0.5 % by weight of strengthening elements selected from Fe, Ti and Cr; and the balance being Cu and inevitable impurities; subjecting the cast material to a solution treatment at a temperature of 800°C or higher, cooling at a rate of 20°C/s or more at least in the temperature range of 800°C to 600°C, subjecting the cooled material to finishing working of 5 to 40 %, and applying aging treatment to the worked material at a temperature of 300 to 460°C. A method for producing a beryllium - copper alloy according to claim 2 wherein the said cast material is subjected to hot working and/or cold working prior to the said solution treatment.

Inventors: HIRAMITSU HIROYUKI, ISHIGURO YOSHIHISA, ISHIKAWA SHUHEI, YASHIRO KAZUMASA, HIRAMITSU, HIROYUKI, ISHIGURO, YOSHIHISA, ISHIKAWA, SHUHEI, YASHIRO, KAZUMASA
Applicants: NGK INSULATORS LTD, NGK INSULATORS, LTD.
Application year: 1994
Main classification: C22C9
IPC codes: C22C9, C22F1